It'll be too obvious to compare the Core 2 Quads to today's Ivy Bridge. But in essence, if you think you have the money to upgrade, go for it. There's no waiting in technology at certain times, just remember that.

They're faster for sure, but my Q6600 still perform really well in all games so for me, i'll not upgrade for now, but i think to upgrade next year with the next Intel Generation...

PS: If you're not overclocked, you can overclock and you'll see an enormous difference !! (Had mine 2.4 @ 4.05 for years now but i know you can easily reach the 10-15% overclock without overvoltage on these kind of chips my 2.4 reach 3.45 with only 1.425V Stock VID is 1.3125)

What are you planning to do? If you got a high end shiny new card then upgrading from an Core 2 Quad would be noticable. Likewise, I have two comparible builds. One with an AMD Phenom I 9850 BE and a i7 2600K. Both having the same video card (HD 6770), there would be almost a 20FPS difference sometimes in games.